The term "molecular drag pump" is used to mean a rotary mechanical pump having fins or of the Holweck type or a combination of both.
In numerous applications, in particular in the field of instrumentation, molecular drag pumps must have a very low level of vibration.
It is known to provide radial vibratory isolation by means of an elastomer O-ring disposed around ball bearings.
In the axial direction, at least one of the ball bearings presses against a shoulder of the stator, with this contact serving as an axial positioning reference determining axial clearances between the rotor and the stator. The contact shoulder operates in shear under the effect of an axial load. Unfortunately, the oscillating system constituted by the rotor pressing against the shoulder via the ball bearings is very stiff, so its resonant oscillation frequency is in the range of nominal speeds of rotation for pumps.